Heart stimulation apparatus and method of testing its installation

ABSTRACT

Heart stimulation apparatus, which is constructed as an implantable unit including a heart stimulator, terminal electrodes of the heart stimulator connectable to a patient&#39;&#39;s heart and a number of different shunts connected in parallel across the terminal electrodes each shunt having a separate remotely operable isolating switch, operable magnetically and a Zener diode, the known trigger voltage of each Zener diode being different. In use the shunts are remotely switched magnetically from the exterior of the patient, starting from the shunt of highest trigger voltage, until an electrocardiograph connected to the patient indicates a change in the voltage reading corresponding to the one of the known trigger voltages. It is thus possible to determine the value of the pulse potential of the heart stimulator. By switching in, for a short time, a shunt having relatively low trigger voltage, the stimulation threshold of the patient&#39;&#39;s heart can be determined.

United States Patent Gaillard Apr. 2, 1974 [75] Inventor: Robert MauriceGeorges Gaillard,

Paris, France [73] Assignee: LElectronique Medicale S.E.R.D.A.L. S.A.,Paris, France [22] Filed: Dec. 27, 1972 [21] Appl. No.: 318,938

[30] Foreign Application Priority Data Dec. 28, 1971 France 71.47064[52] US. Cl 128/419 P, 128/421 [51] Int. Cl A6ln 01/36 [58] Field ofSearch 128/419 P, 421

[56] References Cited UNITED STATES PATENTS 3,638,656 2/1972 Grandjeanet a1 128/419 P 3,693,627 9/1972 Berkovits 3,517,663 6/1970 Bowers et a1128/419 P Primary Examiner-Kyle L. Howell Attorney, Agent, orFirm-Cushman, Darby &

Cushman [57] ABSTRACT Heart stimulation apparatus, which is constructedas an implantable unit including a heart stimulator, terminal electrodesof the heart stimulator connectable to a patients heart and a number ofdifferent shunts connected in parallel across the terminal electrodeseach shunt having a separate remotely operable isolating switch,operable magnetically and a Zener diode, the known trigger voltage ofeach Zener diode being different. In use the shunts are remotelyswitched magnetically from the exterior of the patient, starting fromthe shunt of highest trigger voltage, until an electrocardiographconnected to the patient indicates a change in the voltage readingcorresponding to the one of the known trigger voltages. It is thuspossible to determine the value of the pulse potential of the heartstimulator. By switching in, for a short time, a shunt having relativelylow trigger voltage, the stimulation threshold of the patients heart canbe determined.

10 Claims, 4 Drawing Figures EAYENTEU APR 2 I974 FIG.1.

FIG.3.

HEART STIMULATION APPARATUS AND METHOD OF TESTING ITS INSTALLATION Thepresent life relates to a heart stimulation apparatus and to a method oftesting the installation thereof, in order to detect the lowering andthe inadequacy of the voltage supplied to the heart electrodes, whichcould place the lift of the patient in grave danger.

A check on the functioning of conventional implanted heart-stimulatorsis usually carried out by examining electro-cardiograms obtained fromvoltages picked up at many points on the surface of the patients body.It is thus proposed not only to check that the heart is being stimulatedsatisfactorily at a given instant, but also to analyse the stimulatingpulse collected in the electro-cardiographic shunt, this analysis beingused to detect possible defects such as a drop in the voltage of thebatteries which supply the stimulators or a malfunctioning of thestimulator itself. However, this method only makes it possible to know,very roughly, the voltage actually applied to the electrodes implantedin the heart. In effect, the voltage picked up in theelectro-cardiographic pick-up shunt corresponding to the stimulatingpulse depends on a large number of factors, especially the distancebetween the stimulating electrodes and especially the orientation of theelectrical axis of these two electrodes relative to the pick-up shunt ofthe electro-cardiograph.

According to one aspect of the invention there is provided a method oftesting the installation of a heart stimulator within the body of apatient, such method comprising providing a plurality of voltagetriggered conducting shunts, each having a separate remotely operableisolating switch, and connected in parallel across the terminalelectrodes of the heart stimulator, the known trigger voltage of eachshunt being different, connecting an electro-cardiograph to the heart ofthe patient, remotely switching said shunt in turn from the exterior ofthe patient, starting with a shunt of the highest trigger voltage untilthe electro-cardiograph indicates a change in the voltage readingcorresponding to one of the known trigger voltages, and thus determiningthe value of the pulse potential of the heart stimulator.

With this method it is possible firstly to measure the amplitude of thepulse of the stimulator, in other words to know its actual value at thelevel of the stimulation, and secondly, to make it possible to assessthe margin of stimulation between the physiological requirement and theoperational condition of the apparatus placed in the human body.

Thus by applying a known low voltage to the heart electrodes by means ofan external signal of short duration, a proportionality can beestablished between the corresponding voltage set up in theelectro-cardiogram and the initial voltage set up, which corresponds toan unknown value, which varies with time, of the voltage produced by theheart-stimulator.

The method also consists of switching in for a short time a shunt havinga sufficiently low level, for to stop the stimulation in such a way asto test the stimulation threshold of the heart.

The invention also provides heart stimulation apparatus comprising, asan implantable unit, a heart stimulator having terminal electrodesconnectable to a patients heart, a plurality of shunts connected inparallel across said terminal electrodes, each shunt including aseparate remotely operable isolating switch and triggerable conductingmeans, the known voltage to trigger each shunt being different.

To form the switch, tube relays with low inertia contacts, controlled bya magnetic field, may be used, these contacts being connectedelectrically in parallel and switching in one of a number of shunts,provided with a triggerable conductor, e.g., a diode of the Zenertype,'the various shunts having different triggering voltages from oneanother, the output of these diodes being connected to the other heartelectrode, whilst outside the body of the patient there is a magnet forselctively actuating the relays.

The tube relays are preferably flexible reed relays, although it ispossible also to use other types, such as ball relays or mercury relays.

In order that the invention will become more fully understood, thefollowing description is given by way of example only, reference beingmade to the accompanying drawing, in which:

FIG. 1 is a circuit diagram of the voltage apparatus according to theinvention, shown implanted and with an electro-cardiograph connected tothe patient FIG. 2 is a schematic view of one arrangement of the switchrelays;

FIG. 3 is a schematic view of another arrangement of the switch relays;and

FIG. 4 is a diagram illustrating a voltage pulse as appearing on theelectro-cardiograph plot.

It is apparent from studying FIG. 1 that the heart stimulator l, whichcontains a supply battery which is not shown, supplies, at its terminals0 and b, a voltage to a circuit connected to the electrodes c and d ofthe patients heart 2.

'The human body is generally represented by a volume V, at the surfaceof which voltage tappings e and f are located and are connected to anelectrocardiograph 3, the recorder 4 of which receives the detectedpulses 5. The steeply ascending voltage pulses supplied to the terminalsa and b are of the order of 6 volts. They last for between 1 and 2milliseconds, and provide a current of the order of 2 or 3 milliamperes.On the electro-cardiograph, it is possible to measure,

-for example, pulses ofthe order of l Oll millivolts. As

shunts in the circuit, from the conductor joining terminal a to contact0 on the one hand, and from the conductor joining terminal b to contactd on the other hand, there are located three parallel branches each ofwhich contains a flexible reed relay R R and R the contacts of whichare, on the one side, a,, a, and a;,, connected to the conductor ac. Onthe other side, each of the contacts is connected to a Zener diode, Z Zand Z;,, the outputs of which are respectively b,, b and b and are allconnected to the abovementioned conductor bd. The trigger voltages ofthe Zener diodes are, for example, respectively 4.5. volts for 2 3 voltsfor 2 and 1.5 volts for Z By causing an external magnetic field to actselectively on the three relays R R and R it is thus possible to cut offthe output voltage of the heart-stimulator to one of the three voltagelevels which have just been indicated.

Referring to FIG. 4, which represents the picked up pulse 5 on a largerscale, the initial voltage which appears and which corresponds to anunknown voltage level at the terminals ab has been denoted by T If therelay R is employed, a voltage U, is picked up which corresponds to thetrigger voltage of 4.5 volts of the circuit of the electrodes. By asimple proportionality rule between 4.5 volts and the measured value ofU and the measured value of T it is possible to deduce the actual valueof the normal operating voltage which appears at the terminals ab.However, if it so happens that the triggered voltage introduced via R,is too high, that is to say that it is greater than the actual operatingvoltage T no triggering of diode Z takes place. A second switch relay Ris then closed in place of switch relay R to carry out the sameoperation, represented in FIG. 4 by the voltage U the triggered voltageof diode Z read on the electro-cardiograph with T being the voltage readwhich represents the actual voltage of the stimulator. In addition, athird triggered voltage level corresponding to the trigger voltage ofdiode 2;, can be provided, which gives a read voltage U this levelbeing, in every case, greater than the excitation threshold of the heartat the time when the apparatus was placed in position, but which issufficiently low subsequently to detect, due to inadequate stimulation,an increase in the stimulation threshold of the heart at this same levelU Moreover, it is possible to have a larger number of relays in order tohave several intermediate thresholds. If it has already been found thatthe operating voltage is, for example, T corresponding to the actualvoltage at the terminals, the voltage margin available to the heartstimulator will be known by the difference L T U If this margin were toosmall, a surgical operation would be necessary to give the heartstimulator more energy. Thus a calibration of the heart stimulator isobtained, that is to say the difference between the energy which isgiven and that which is required by the organism, or alternatively theactual difference which exists between the signal which is applied andthe threshold for stimulating the myocardium.

FIG. 2 represents a possible arrangement for the flexible reed relays RR and R enclosed in a space in the body, symbolized by E Thelongitudinal axes of the relays are arranged radially with angles of 45between them. A magnet 6 placed outside the body, can pivot about itspole corresponding to the point where the relay axes meet, and due tothis pivoting it will be possible to actuate in turn the relays R R andR According to the arrangement of FIG. 3, the space E contains the threerelays R R and R placed in a parallel arrangement. This parallelarrangement can, moreover, be spread out widthwise or depthwise. In thecase of a widthwise spreading, the magnet 6 will undergo a paralleltranslation in order to excite the three relays in succession. In thecase where the relays (possessing equivalent magnetic sensitivities)were spread apart depthwise, they could be actuated in succession bygradually bringing the magnet closer. This gradual approach can alsocontrol relays which are placed side by side at the same depth but whichpossess different magnetic sensitivities. This technique for excitingthe flexible reed relays comprises, furthermore, measures for preventingthe inopportune excitation of the relays by lines of force which are toodistant from the magnet, but it is not necessary to describe this knowntechnique in more detail.

of course, the process of the invention can be applied to any implantedsystem for supplying a heart stimulator and the device described abovecan be constructed in various ways without departing from the spirit ofthe invention.

I claim:

1. A method of testing the pulse potential appearing at the terminalelectrodes of a heart stimulator within the body of a patient, saidmethod comprising the steps of providing a plurality of voltagetriggered conducting shunts, each having a separate remotely operableisolating switch, and connected in parallel across said terminalelectrodes, the known voltage to trigger each shunt being different,connecting an electrocardiograph to the patient, remotely switching saidshunts in turn from the exterior of the patient, starting with a shuntof the highest trigger voltage, until the electrocardiograph indicates achange in the voltage reading corresponding to one of the known triggervoltages, and thus determining the value of the pulse potential of theheart stimulator.

2. A method as claimed in claim 1, and further comprising the step ofswitching in for a short time, a shunt having a sufficiently low triggervoltage so as to test the stimulation threshold of the heart.

3. A method as claimed in claim 1, wherein the remote switching of theshunts is effected magnetically.

4. Heart stimulation apparatus comprising, as an implantable unit, aheart stimulator, terminal electrodes of said heart stimulatorconnectable to a patients heart, a plurality of shunts connected inparallel across said terminal electrodes, each shunt including aseparate remotely operable isolating switch and triggerable conductingmeans, the known voltage to trigger each shunt being different.

5. Heart stimulation apparatus as claimed in claim 4, wherein saidtriggerable conducting means comprise Zener diodes.

6. Heart stimulation apparatus as claimed in claim 4, wherein saidremotely operable isolating switches each comprise a relay of themagnetically operable sealed tube flexible reed type.

7. Heart stimulation apparatus according to claim 6, wherein threerelays are employed, which are arranged radially whereby the closing ofsaid switches may be achieved by pivoting a magnet successively oversaid relays.

8. Heart stimulating apparatus as claimed in claim 6, wherein threerelays are employed arranged in parallel directions to one another, theswitching being effected by corresponding translational movement of themagnet.

9. Heart stimulating apparatus as claimed in claim 6, wherein threerelays of different magnetic sensitivity are employed said relays beingarranged in parallel, whereby the selective switching may be achieved bybringing the magnet closer or taking it further away from the patientsbody.

10. Heart stimulation apparatus as claimed in claim 6, wherein threerelays of equivalent magnetic sensitivities are employed these beingarranged so as to be adapted to be disposed at different depths in thepatient.

1. A method of testing the pulse potential appearing at the terminalelectrodes of a heart stimulator within the body of a patient, saidmethod comprising the steps of providing a plurality of voltagetriggered conducting shunts, each having a separate remotely operableisolating switch, and connected in parallel across said terminalelectrodes, the known voltage to trigger each shunt being different,connecting an electrocardiograph to the patient, remotely switching saidshunts in turn from the exterior of the patient, starting with a shuntof the highest trigger voltage, until the electrocardiograph indicates achange in the voltage reading corresponding to one of the known triggervoltages, and thus determining the value of the pulse potential of theheart stimulator.
 2. A method as claimed in claim 1, and furthercomprising the step of switching in for a short time, a shunt having asufficiently low trigger voltage so as to test the stimulation thresholdof the heart.
 3. A method as claimed in claim 1, wherein the remoteswitching of the shunts is effected magnetically.
 4. Heart stimulationapparatus comprising, as an implantable unit, a heart stimulator,terminal electrodes of said heart stimulator connectable to a patient''sheart, a plurality of shunts connected in parallel across said terminalelectrodes, each shunt including a separate remotely operable isolatingswitch and triggerable conducting means, the known voltage to triggereach shunt being different.
 5. Heart stimulation apparatus as claimed inclaim 4, wherein said triggerable conducting means comprise Zenerdiodes.
 6. Heart stimulation apparatus as claimed in claim 4, whereinsaid remotely operable isolating switches each comprise a relay of themagnetically operable sealed tube flexible reed type.
 7. Heartstimulation apparatus according to claim 6, wherein three relays areemployed, which are arranged radially whereby the closing of saidswitches may be achieved by pivoting a magnet successively over saidrelays.
 8. Heart stimulating apparatus as claimed in claim 6, whereinthree relays are employed arranged in parallel directions to oneanother, the switching being effected by corresponding translationalmovement of the magnet.
 9. Heart stimulating apparatus as claimed inclaim 6, wherein three relays of different magnetic sensitivity areemployed said relays being arranged in parallel, whereby the selectiveswitching may be achieved by bringing the magnet closer or taking itfurther away from the patients body.
 10. Heart stimulation apparatus asclaimed in claim 6, wherein three relays of equivalent magneticsensitivities are employed these being arranged so as to be adapted tobe disposed at different depths in the patient.